Retractors of all shapes and sizes have been present since the dawn of surgery. A common type of retractor is the chest retractor or thoracic retractor. Retractors of this category may comprise sternum retractors, thoracotomy retractors, mini-thoracotomy retractors, mini-sternotomy retractors, and retractors used for the surgical harvesting of internal thoracic arteries through a sternotomy or intercostal approach incision. For instance, such internal thoracic arteries may comprise the left internal mammary artery.
Sternum retractors are commonly used in cardiac surgery. Cardiac surgery may take several forms. For instance, these forms include traditional coronary artery bypass graft surgery (CABG) requiring the heart-lung machine, CABG surgery performed directly on a beating heart, minimally invasive direct coronary artery bypass surgery (MIDCAB), heart valve repair surgery, heart valve replacement surgery and surgery to correct a septal wall defect, whether atrial or ventricular. Thoracic retractors serve to incise, penetrate and retract the thoracic structure, namely the surface, underlying tissue and bone structure of a patient, in order to access the body organs and internal body tissue contained within the patient's thorax. In the case of a sternum retractor, the thoracic structure in question is the patient's sternum and entire ribcage. The body organs and internal body tissue exposed by use of a sternum retractor will comprise the coronary organs, which include in particular the heart, the heart's arteries and veins, the surrounding tissue and vessels, the pericardium, the thymus, the pleura, and any other tissue within the mediastinum or the space between the two lungs. Sternum retractors are typically used in CABG surgeries or valve replacement surgeries.
The drive in recent years for less invasive cardiac surgery has resulted in smaller chest incisions and consequently smaller chest retractors as well. In minimally invasive cardiac surgery, such as MIDCAB, mini-thoracotomy retractors were introduced to laterally retract a pair of adjacent ribs and expose the underlying coronary organs through the resultant intercostal space.
Most known chest retractors have an elongate rack bar and two retracting arms, namely a fixed retracting arm and a movable retracting arm. Both arms typically extend in a direction substantially normal to the rack bar. The movable arm can be displaced along the rack bar using a crank, which also acts as a torque lever, to activate a pinion mechanism. Two blades are provided, usually below the retractor arms, to interface with the patient's sternum or skin, and which forms part of the thoracic structure. The basic design and mechanism for separating the two or more spreader members or retractor arms of chest retractors have remained relatively unchanged since the first introduction of retractors in cardiac surgery. Consequently, cardiac surgeons have developed a manual proficiency in using the current retractors.
In all chest retractors, there is a resistance to retraction by the patient's thoracic structure and by the retractor itself, which the surgeon must overcome in deploying the retractor to expose the coronary organs. The separating force the surgeon applies is mainly a function of the geometry of the rack and pinion mechanism, the length of the retractor arm, and the friction at the interface between all moving components in the retractor assembly. The separating force to overcome the resistance load on the retractor may at times be excessive since:                a patient may be very corpulent;        a patient's bones may be very brittle, and therefore especially resistant to rotation of the ribs about the spine;        the retractor blade design may result in concentrated loads being generated at locations remote from the rack bar and pinion mechanism;        friction in the retractor system may be high; and        wear may have occurred at the mechanical interface between moving components.        
The deployment of the retractor, and more specifically the relative movement of the retractor arms, may at times be intermittent, or “jerky” and not smooth, since:                the thoracic structure generally imposes variable loads on the retractor as a function of its retracted opening;        the meshing of the crank and pinion mechanism of the retractor may not be continuous, such that the load at the crank handle may vary as a function of the pinion position within the rack grooves and consequently as a function of the circumferential orientation of crank handle;        the load to overcome friction between retractor components to set retraction in motion is typically higher than the load to keep said components in motion;        friction between moving retractor components may be subject to variation given uneven wear in components; and        the friction forces associated with the operation of the retractor are normally linked to the resistance force exerted by the thoracic structure, which is itself variable as a function of its retracted opening.        
In most chest retractors, the pinion mechanism usually consists of two pins which engage the rack teeth within grooves formed therebetween in a variety of orientations depending on the rotation of the pinion assembly (and the crank handle usually attached to the pinion assembly). This results in a substantially stable orientation when both pins are engaged with the rack teeth, and a substantially unstable orientation when only one pin is engaged with a rack tooth. This also results in an alternation of discrete and substantially stable locked positions with unstable unlocked positions of the retractor arms along the entire length of the rack.
Based on the foregoing, it would therefore be advantageous to provide a surgical retractor, for instance a sternum retractor, with easier deployment in cardiac surgery.
Thus, it is one object of the present invention to attempt to reduce the separating force and torque the surgeon must apply to the retractor, to effect retraction in surgery.
It is a further object of the present invention to seek to maintain more uniform separating loads by normalizing the variables in chest retractor design discussed above and experienced during deployment in surgery.
It is a further object of the present invention to aim to reduce the risk of injury to a patient by providing improvements to retractors, for instance sternum retractors, that allow the surgeon to deploy said retractors in a controlled manner free from sudden or intermittent movements.
It is a further object of the present invention to provide a chest retractor, for instance a sternum retractor, which may more readily be cleaned and sterilized.
It is a further object of the invention to provide a retractor design which is intended to reduce concentrated loads sometimes found at the extremities of a surgical incision, when compared to certain prior art retractors, and for a given retracted opening in the thoracic structure when measured at the mid length location along the incision.
It is a further object of the present invention to provide a chest retractor with contoured retractor blades adapted to more closely conform to the ribcage halves along a sternotomy incision as the thoracic structure is retracted.
It is an additional object of the present invention to provide a retractor having a continuous variable range of lockable open retracted positions.
It is an additional object of the present invention to retrofit existing retractors, for instance sternum retractors, with improvements that aim to reduce and normalize separating loads which the surgeon must apply during retraction of the thoracic structure therewith.
It is an additional object of the present invention to apply the concepts and principles of this invention, as they relate to chest retractors and more specifically to sternum retractors, to other types of retractors.
These and other objects of the present invention will become apparent from the description of the present invention and its preferred embodiments which follows.